Fuel injection controlling system for internal combustion engine

ABSTRACT

A fuel injection controlling system for internal combustion engines, wherein the various conditions of the internal combustion engine are converted to signal currents, these signal currents are superimposed upon a timing signal current, the magnitude of which corresponds to a lapse of time, and then supplied to an input terminal of a current level detecting circuit so that there is produced an output pulse signal of which the duration is related to the quantity of fuel required by the internal combustion engine, and a fuel injection valve is opened in accordance with said output pulse signal thereby to control the quantity of fuel supplied to the internal combustion engine.

[ 1 Jinn. 25, 19%

[54] FUEL INJECTION @DNTROLUNG 3,240,191 3/1966 Wallis 123/32 E1 SYSTEM [20R INTERNAL 3,483,851 12/1969 Reichardt..... ....l23/32 E1 3,456,628 7/1969 Bassot et al..... ...l23/1l9 X CUMBUSTHUN ENGINE 3,463,130 8/1969 Reichardt et a1 HIM/139.17 [72] Inventors: Seiji Suda; Masayulti lshizalri, both of Hitachi-shi, Japan Primary Examiner- Laurence M. Goodridge A t 11' d 1731 Assignee: 1111mm, Ltd., Tokyo, Japan chug one t 22 Filed: Apr. 11, 1969 1 1 BSTRACT 211 App] 15 320 A fuel injection controlling system for internal combustion engines, wherein the various conditions: of the internal combustion engine are converted to signal currents, these signal {301 Foreign Application Priority Data currents are superimposed upon a timing signal current, the Apr. 17, 1968 Japan ..43/25206 magnitude which CoireSPOnds a lapse of iime and Sept 1 l 1968 Japan "43/611960 supplied to an input terminal ofa current level detecting circuit so that there is produced an output pulse signal of which 52 us. 01 ..123 32 EA 123/139 E 123/119 is ieiaiei quaiiiiiy iuei required by 51 int. c1 .1 ..r02m 51 02 imemai combusiimi engine and a mi injection vaive is [58] Field of Search 32 E 32 El 119 139 E opened in accordance with said output pulse signal thereby to control the quantity of fuel supplied to the internal com- [56] References Cited busuon engine" UNITED STATES PATENTS 12 Claims, 12 Drawing Figures 3,005,447 10/1961 Baurnann et a1 ..123/119 PATENTED JANZS I572 SHEET 3 OF 3 INVENTORS MASA YMHI IISHI A Kl.

Si l TI SUD l BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a fuel injection controlling system for internal combustion engines which is adapted to control the quantity of fuel to be supplied, and more particularly it pertains to improvements in or relating to a system of electrically controlling the quantity of fuel to be injected.

2. Description of the Prior Art Among the conventional methods of supplying fuel to an internal combustion engine are the methods of sucking out fuel by making use of a negative pressure existing in a suction pipe and the method ofinjecting fuel by means of an injection nozzle. In the latter method, the quantity of fuel to be supplied can be accurately controlled in correspondence to the quantity of fuel required by the internal combustion engine so that the efficiency of the internal combustion engine is enhanced to provide an increased output torque and the quantity of harmful exhaust gas is decreased. Thus, this method is effectively utilized as means for supplying fuel to the internal combustion engine for an automobile.

In most of the injection-type fuel feed systems, the various conditions of the internal combustion engine are imparted to electric elements in order that an electrical signal having a magnitude corresponding to the quantity offuel to be supplied to the internal combustion engine may be produced by making use ofa change in the time constant of a time constant circuit constituted by such electric elements or a potential variation in a voltage divider circuit, and an electromagnetic valve is ac tuated in accordance with the electrical signal thus produced, thereby controlling the quantity of fuel which is injected by an injection nozzle. A typical example of such systems is a method opening an electromagnetic valve by means of an electrical signal having a required duration which is produced by the use ofa monostable flip-flop circuit. In this method, the values of the capacitor and resistor serving as timing means in the monostable flip-flop circuit are varied in accordance with the conditions of the internal combustion engine thereby to change the duration of the output. Such a system is disclosed in the US. Pat. No. 2,941,519 to Zechnall et al., filed Dec. 1, 1958, and US. Pat. No. 3,051,152 to Paule et al., filed Sept. 17, 1958, for example. In this system, however, a limitation is put on the conditions of the internal combustion engine from which the quantity of fuel is to be determined, since difficulty is encountered in an attempt to constitute the timing means by a number of electric elements in the monostable flip-flop circuit. In order to determine the quantity of fuel from a number of conditions, it will become necessary to resort to the use ofa complicated composite mechanism.

Another example is a system designed so that the various conditions of the internal combustion engine are converted to resistance values, a signal voltage is provided by an operational means (voltage divider circuit) which is constituted by connecting a combination of said resistance values between power source lines, and that the open duration of an electromagnetic valve is controlled in accordance with the signal voltage thus provided. Such system is disclosed in US. Pat. No. 3,240,191, to Wallis, filed May 29, 1963, for example. With the system using operational means as described above, however, it is very difficult to change the resistance charac teristics corresponding to the various conditions of the internal combustion engine since the absolute values of such resistances have effect on the entire voltage distribution. Thus, this makes it difficult to achieve the matching between various types of internal combustion engines to which such system as described above is applied. For internal combustion engines for automobiles, such matching difficulty constitutes a great disadvantage from the standpoint of mass production.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a system capable of controlling the quantity of fuel to be supplied by effecting an operation with respect to electric signals corresponding to the various conditions of an internal combustion engine in a very simple manner.

Another object of the present invention is to provide such a system that can be matched to a plurality of types of internal combustion engines having different characteristics merely by making minor adjustments or design changes.

The system according to the present invention is characterized in that the various conditions of an internal combustion engine from which the required quantity of fuel is determined are converted to independent electric signals respectively, a time signal is produced which corresponds to the lapse of time from the moment when the crankshaft reaches a predetermined position, these signals are combined with each other and then supplied to a discriminator circuit to produce an output signal having a time width corresponding to the required quantity of fuel, and an electromagnetic valve is operated in accordance with the output signal thus produced.

Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE INVENTION FIG. lla is a graph showing the relationship between the negative pressure in the manifold and the quantity of fuel to be supplied;

FIG. 1b is a graph showing the relationship between the rotational frequency of the engine and the quantity of fuel to be supplied, with the negative pressure in the manifold maintained constant;

FIG. 1c is a graph showing the relationship between the engine temperature and the quantity of fuel to be supplied;

FIG. 2a is a circuit diagram showing an example of discriminator means according to the present invention;

FIG. 2b is a view showing the input current characteristics of said discriminator means;

FIG. 3a is a circuit diagram showing an example of arithmetic operating means according to the present inventron;

FIG. 3b is a view showing the characteristics thereof;

FIG. 4 is a circuit diagram showing the fuel injection controlling system for internal combustion engines according to an embodiment of the present invention;

FIGS. 5a and 5b are views showing characteristic curves useful for explaining variations of fuel feed characteristics with the negative pressure in the manifold, respectively;

FIG. 6a is a circuit diagram showing another example of dis criminator means according to the present invention; and

FIG. 6b is a view showing the characteristic curves thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred quantity Q, of fuel to be supplied in terms of the negative pressure P in the manifold of the internal combustion engine is as shown in FIG. la from which it will be seen that the quantity 0,, in terms of the negative pressure P is represented by a continuous characteristic curve. However, it is difficult to change the supplied fuel quantity Q, along such a characteristic curve. In practice, therefore, such a characteristic is approximated by polygonal line. The negative pressure P in the manifold depends upon the opening degree of the throttle valve and the rotational frequency N of the internal combustion engine. At a predetermined rotational frequency N, if the negative pressure P in the manifold is low, then it is required that the opening degree of the throttle valve be increased to provide an increased output. In this region, therefore, the characteristic is made such that the supplied fuel quantity Q is so selected as to produce a maximum output in disregard of fuel cost. In case the negative pressure P in the manifold is high, however, the opening degree of the throttle valve is low. In this region, therefore, the characteristic is modified so that the supplied fuel quantity Q, is selected to make the fuel cost the lowest possible. The modification point corresponds to the bent P. of the polygonal line. Thus, the characteristic is divided into a power region and an economic region, with this bent point as a boundary.

Referring now to FIG. 1b, there is shown the characteristic of the proper supplied fuel quantity O in terms of rotational frequency N of the engine. This characteristic also changes in the form of a curve in terms of the rotational frequency N, with the manifold negative pressure P as parameter. In practice, however, it is difficult to achieve control along such curve. Therefore, it is approximated by straight line.

FIG. 10 shows the characteristic of supplied fuel quantity Q, in terms of engine temperature T. TI-lis characteristic is also approximated by a polygonal line since in some temperature region the quantity Q, is proportional to the engine temperature while in the opposite end regions there occur saturation characteristics. I

In order to control the quantity Q of fuel to be supplied in the injection-type fuel feed system, two methods are conceivable, that is, a method to change the quantity of fuel to be injected per unit of time and a method to change the duration of the fuel injection. In order to control such changes with the aid of an electromagnetic valve, the latter method turns out to be advantageous. The system according to the present invention may be applied to such a control.

In such method, the quantity Q of fuel to be supplied and the opening duration 2 of the electromagnetic valve are in substantially linear relationship with each other. If the supplied fuel quantity Q is represented in terms of duration 2, then it may be considered that the duration 1 is represented by a function including as independent variables the manifold negative pressure P, rotational frequency N and temperature T.

=f1( )+fz( )+fi( (1) From manifold negative pressure P corresponding to each bent point,f,,f andf vary as follows:

When P P When P P WhenP P and T T 7",,

f t T)=kT+k' e) where T represents the temperature corresponding to the low-temperature bent point and 7, indicates the temperature corresponding to the high-temperature bent point.

in accordance with the present invention, the aforementioned manifold negative pressure P, rotational frequency N and temperature T are converted to signal currents from which it is attempted to determine the opening duration t of the electromagnetic valve.

Description will now be made of the principle of an embodiment of the present invention, with reference to FIGS. 2a, 2b and 3a, 3b.

Referring to FIG. 2a, there is shown a discriminator circuit comprising an NPN-transistor l and a tunnel diode 2 connected between the base electrode and the emitter electrode of the transistor 1 in the same polarity and in parallel with the latter, wherein the base electrode of the transistor 1 is connected with an input terminal 3, and the collector electrode thereof is connected with a power source terminal 5 through a load resistor 4. The operation of this discriminator circuit will be explained with reference to FIG. 2b. If an input current I, arriving at the input terminal 3 is increased, then the overall current is enabled to flow through the tunnel diode 2 because of the fact that the tunnel diode represents a very low internal impedance when the input current I,,, is lower than the maximum value I of the tunnel diode 2, so that thecurrent is not caused to flow in the base electrode of the transistor 1. Thus, the nonconductive state is established between the emitter and the collector of the transistor. However, if the input current I. exceeds the maximum value I,,,, then the tunnel diode 2 is caused to enter the negative region so that the current flowing therethrough is decreased with the result that the terminal voltage builds up. Consequently, the potential at the base electrode of the transistor 1 increases to cause a current l to flow between the base electrode and the emitter electrode. Thus, the conductive state is established between the emitter electrode and the collector electrode so that a collector current is caused to flow so that an output signal is obtained across the load resistor 4.

In accordance with one embodiment of the present invention, an attempt is made to effect operation with respect to the optimum quantity of fuel to be supplied to the engine from the various signal currents by making use of the aforementioned characteristic.

FIG. 3a is a circuit diagram showing an example of operational means adapted to form an output signal corresponding to a required duration t by imparting the various conditions of the internal combustion engine to the discriminator circuit described above in connection with FIGS. 2a and 2b. Numeral 6 represents a signal input terminal corresponding to the rotational frequency N of the engine, 7 a signal input terminal corresponding to the manifold negative pressure P, 8 a signal input terminal corresponding to the temperature T, and 9 a signal input terminal corresponding to the lapse of time. These signal input terminals are connected in common to the input terminal of the discriminator circuit through the resistors 10, ll, 12 and 13 respectively. A capacitor 14 and resistor 15 constitute a differentiating circuit which is connected in series between the power source terminal 5 and the input terminal 3. This differentiating circuit is provided for the purpose of imparting to the input terminal 3 a preparation signal current I, having such a magnitude as to establish the conductive condition between the emitter and the collector electrodes of the transistor 1 when the power source is turned on. Numeral 16 represents a reset signal input terminal for imparting a negative trigger voltage to the transistor 1 to establish the nonconductive condition between the emitter and the collector electrodes of the transistor 1 when it is desired that the fuel injection be started. This reset signal input terminal is also connected with the input terminal 3. An output signal is taken from between an output terminal 17 connected with the collector electrode transistor 1 and the ground.

Next, the operation of the foregoing arrangement will be described with reference to FIG. 3b. First of all, upon application of the power source voltage to the power source terminal 5, the preparation current l is caused to flow into the input terminal 3 through the capacitor 14 and resistor 15 so that a current having a sufficient magnitude to establish the conductive state between the emitter and the collector electrodes of the transistor 1 is caused to flow into the base electrode thereof. At this point, the potential at the collector electrode is so low that no output signal is available from the output terminal 17. Subsequently, if the engine is rotated by starter means (not shown), then a negative pulselike reset current I, is supplied from the input terminal 16 to the input terminal 3 when it is desired that the fuel injection be initiated. This reset current I, reduces the current flowing in the input terminal 3 so that the potential at the base electrode of the transistor 1 is decreased, while at the same time resetting the tunnel diode 2. Thus, the base current of the transistor 1 is interrupted so that the nonconductive condition is established between the emitter and the collector electrodes thereof. As a result, the potential at the collector electrode increases, and thus an output signal B appears at the output terminal 17. At the same time, a sawtooth wave signal voltage which increases with the lapse of time is applied to the signal input terminal 9 so that a time-lapse signal current I is caused to flow through tI-le input terminal by way of resistor 13. Further, voltages corresponding to the various conditions of the engines are applied to the other signal input terminals 6, 7 and 8, and signal currents l,,, I, and I, are supplied to the input terminal 3 through the resistors 10, Ill and 12 respectively. Because of the very low input impedance of the input terminal 3, these signal currents are algebraically combined with each other so that there is obtained a combined current I which in turn flows in the input terminal 3. Such combined current I, is selected to be lower than the maximum value I,,, of the tunnel diode 2. The combined current I increases with an increase of the timelapse signal current 1,, but when it is in the region below the maximum value I,,,, it is caused to flow to the ground through the tunnel diode 2, so that no current is made to flow in the base electrode of the transistor 1. Thus, the nonconductive condition is established between the emitter and the collector electrodes, and therefore in such region, the output signal available at the output terminal 17 is preserved. After the lapse of predetermined time t, however, the combined current I, flowing in from the input terminal 3 exceeds the maximum value l,, of the tunnel diode 2, so that the internal impedance of the tunnel diode 2 is increased with the result that the terminal voltage is increased. Consequently, the potential at the base electrode of the transistor increases to enable a base current to flow therein so that the conductive condition is established between the emitter and the collector electrodes. Thus, the potential at the collector electrode decreases so that the output signal at the output terminal disappears. By operating the fuel injection control value in accordance with the out put signal available at the output terminal 17, therefore, it is possible to feed fuel for the aforementioned duration t. This duration t depends upon the magnitudes of the signal currents I,,, 1,, and l, which depend upon the conditions of the engine, and therefore the quantity Q offuel to be supplied can be controlled to correspond to the required fuel quantity by changing these signal currents in accordance with predetermined characteristics. That is, since the time-lapse signal current I, varies at a constant gradient irrespective of the conditions of the engine whereas the composite current I, flowing in the input terminal 3 varies like I,,,,, 1 the duration 1 in which the maximum value I, of the tunnel diode 2 is reached varies like t 1 t Referring now to FIGS. 5a and 5b, description will be made of the present invention as embodied under the following conditions.

a. Injection is simultaneously effected with respect to respective two cylinders of a fourcylinder, four-stroke-type engine.

b. Injection timing is set such that the injection is started by means of primary current interrupter contact associated with a firing coil and additionally provided with two contacts when these contacts are made.

c. A sawtooth wave voltage which builds up with the lapse of time is used as a signal to detect time variations.

d. It is assumed that the required fuel feed characteristics of the engine are as shown in FIGS. lla, Ilb and I0, and that such characteristics can easily be changed.

In FIG. 4, numeral 118 represents the aforementioned operational circuit, 19 a sawtooth wave generating circuit adapted for providing a time-lapse signal, and 20 a reset circuit adapted to provide a negative trigger voltage in synchronism with the generation of the sawtooth wave. Numeral 21 indicates a circuit for detecting a negative pressure in the engine suction manifold, which consists of a combination of a diaphragm and a potentiometer type resistor, 22 an engine temperature detecting circuit, and 23 a circuit for detecting the rotational frequency of the engine. Numeral 24 denotes a selector circuit for selecting that one of the electromagnetic valves to which the output signal of the operational circuit is to be supplied, and 25 a switching circuit for flowing a driving current through the electromagnetic valve thus selected.

These circuits will be described in further detail below. The sawtooth wave generating circuit 19 is constituted by a bootstrap circuit. When either one of timing contacts 26 and 27 is made, a current which has been flowing through a resistor 29 by way of a resistor 28 is now made to flow to the ground through diode 30 or 31, so that a transistor 32 is rendered non conductive. At this point, a capacitor 35 begins to be charged through a diode 33 and a resistor 34. As a result, the potential at the base electrode of a transistor 36 is increased so that the conductivity between the collector and the emitter electrodes thereof is increased. Thus, an increasizngcurrent is caused to flow from the emitter electrode to a resistor 37, so that the potential at the emitter electrode builds up gradually. By virtue of the fact that the transistor 32 is rendered nonconductive when the sawtooth wave generating circuit 19 starts the generation of the sawtooth wave, the reset circuit 20 is adapted to establish the conducting state between the emitter and the collector electrodes of a transistor 39 by connecting the collector electrode of the transistor 32 with the base electrode of the transistor 39 through a resistor 38, and impart a negative trigger voltage to the reset signal input terminal 16 of the operational circuit by discharging charges stored at a capacitor 40 when the transistor 39 is in the nonconducting state, The engine manifold negative pressure detecting circuit 21 is constituted by the diaphragm adapted for movement in accordance with the manifold negative pressure and potentiometer type resistor 41 actuated by the diaphragm, wherein a voltage which builds up with an increase in the manifold negative pressure is obtained at a slidable contact 42. The engine temperature detecting circuit 22 is: constituted by a series circuit of a temperature-sensitive element 43 and resistor 44, wherein a signal voltage is obtained at the connection point of the series circuit. In the case where as temperature-sensitive element 43 use is made of a thermistor, the resistance value of the temperature-sensitive element 43 decreases with temperature increase, while the potential at the output point thereof increases. The lowest voltage is clamped by resistors 45 and 46 and diode 47, and the highest voltage is clamped by resistors 48 and 49 and diode 50. Thus, there is obtained the characteristic represented by the polygonal line in FIG. lie. The engine rotational frequency detecting circuit 23 is constructed by the use of a monostable flip-flop circuit which is triggered with the aid of a breaker contact 52 for interrupting the primary current flowing through a :firing coil 51, in order to reduce the pulsation of the output voltage and improve the response characteristic. The voltage at the connection point between the firing coil SI and the breaker contact 52 builds up when the contact 52 is in the open state. This voltage is differentiated by a capacitor 53 and resistor 54 and then im parted to the base electrode of a transistor 56 of the monostable flip-flop circuit through a diode 55. Further, this voltage is imparted to the base electrode of a transistor 53 through a resistor 57, thus establishing the conductive condition between the emitter-collector electrodes of the transistor 58. The collector electrode of the transistor 58 is connected with a conductor 60 through a resistor 59 and also grounded through a capacitor 61 and resistor 62. Thus, if the voltage which has been imparted to the base electrode of the transistor 58 becomes extinct due to the closure of the breaker contact 52, then the transistor 58 is rendered nonconductive so that the potential at the collector electrode thereof increases. This voltage variation is differentiated by a capacitor 611 and resister 62, and then imparted to the base electrode of the aforementioned transistor 56 through a diode 63. The transistor 56 constitutes the monostable flip-flop circuit together with a transistor 64, resistors 65, 66 and 68 and capacitor 69. The transistor 56 is rendered nonconductive when the monostable flip-flop circuit is in the stable state, and it has its collector electrode connected with an integrating circuit constituted by a resistor 70 and capacitor '71. At this capacitor 71, there occurs a voltage of which the magnitude corresponds to the rotational frequency N of the engine. This voltage is applied to the base electrode of a transistor '72 to change the conductivity between the emitter and the collector electrodes thereof so that a voltage appearing at the connection point between resistors 73 and 74 connected in series with each other is varied in accordance with the rotational frequency N of the engine.

Series resistors 75 and 76 constitute a clamping circuit together with a diode 77, which is adapted to clamp the maximum value of the voltage appearing at said connection point. The selector circuit 24 consists of a bistable flip-flop circuit constituted by transistors 78 and 79 and resistors 80, 81, 82 and 83. The transistors 78 and 79 are connected in such a manner as to be controlled by the aforementioned timing contacts 26 and 27. Those terminals of the contacts 26 and 27 which are opposite to the grounded ones are connected with the conductor 60 through resistors 84 and 85 respectively, and also with the base electrodes of transistors 88 and 89 through resistors 86 and 87 respectively. The transistors 88 and 89 have their emitter electrodes grounded and the collector electrodes thereof connected with the conductor 60 through resistors 90 and 91 and further with the base electrodes of the transistors 78 and 79 of the aforementioned bistable flip-flop circuit through resistors 101, 102 and diodes 103, 104 respectively. Thus, the transistors 78 and 79 are rendered conductive by the fact that their base electrodes'are biased at a high voltage when one of the contacts 26 and 27 is closed so that one of the transistors 88 and 89 is rendered nonconductive. Description will now be made of the operational circuit 18. The quantity of fuel to be supplied which depends upon the engine manifold negative pressure P and rotational frequency N differs between when the manifold negative pressure P is P P and when P P,,. Therefore, the gradient of the characteristic is changed by changing the resistors 10,1 1 to resistors 10, 1 1 which are connected with input terminals 6 and 7 through switches SW2-1 and SW2-2 which are operated when the manifold negative pressure P is equal to P The state shown in the drawing corresponds to that in which the manifold negative pressure P is P P The values of the resistors and 11 are selected to be lower than those of the resistors 10 and 11', and the gradient of the characteristic is so set up that variations in the current flowing in the input terminal 3 become greater as compared with those in the manifold negative pressure, as shown in FIG. 5a. By changing the values of the resistors, the gradient of the characteristic is changed as described above, but the absolute value is also varied at the same time. If it is left as it is, the quantity of injected fuel in terms of the manifold negative pressure P is changed in a jumping manner when P=P Such phenomenon is undesirable. Therefore, the design is made such that this jumping phenomenon is prevented by switching from a resistor 108 to a resistor 108 a bias current flowing in the input terminal 3 through a switch SW2-3 from an input terminal 107 to which is applied a fixed bias voltage available from the connection point between the series resistors 105 and 106 as input. The output terminal 17 of the operational circuit 18 is coupled to the base electrode of a transistor 110 through a resistor 109. The transistor 110 which is adapted to serve as amplifier has its collector electrode connected with the conductor 60 through a resistor 111 and its emitter electrode connected with the base electrode of a transistor 113 for driving an electromagnetic valve. The collector electrode of the transistor 112 is connected with the conductor 60 through electromagnetic coils 113 and 114, and the emitter electrode thereof is grounded. On the other hand, the output terminal 17 is connected with the base electrode of a transistor 116 through a resistor 115. This transistor 116 which is also adapted to serve as amplifier has its collector electrode connected with the conductor 60 through a resistor 117 and its emitter electrode connected with the base electrode of a transistor for driving an electromagnetic valve. The collector electrode of the transistor 118 is connected with the conductor 60 through electromagnetic coils 119 and 120, and the emitter electrode thereof is grounded. Further, the base electrodes of the two amplifier transistors 110 and 116 are connected with the collector electrodes of the transistors 78 and 79 of the aforementioned discriminator circuit 24 through diodes 121 and 122 respectively. SW1 is a power source switch connected between the conductor 60 and a battery 123.

Next, the operation of the present system will be fully described. First of all, by closing the power source switch SW1, the voltage of the battery is applied to the entire circuit arrangement so that the latter is brought into the active state. In the operational circuit, when the voltage at the power source terminal 5 builds up, the preparation current I, is caused to flow in the input terminal 3 through the capacitor 14 and resistor 15 to render the transistor 1 conductive so that no output voltage appears at the output terminal 17. Thus, none of the transistors and 116 can be rendered conductive, and therefore the electromagnetic valves remain closed. At the same time, signal voltages corresponding to the engine manifold negative pressure P, rotational frequency N and temperature T and imparted to the input terminals 6, 7 and 8 respectively, so that currents corresponding to these voltages are supplied to the input terminal 3. When the engine is started, either one of the timing contacts 26 and 27 is made at a point of time when it is desired that the fuel injection be initiated. In case the timing contact 26 is made for example, the bias current which has been flowing from the conductor 60 to the transistor 32 through the resistors 28 and 29 is now caused to flow to the ground through the diode 30 and timing contact 26, so that the transistor 32 is rendered nonconductive. As a result, the potential at the collector electrode of the transistor 32 increases to render the transistor 39 conductive so that the electric charges which have been stored at the capacitor 40 are discharged to the input terminal 16 of the operational circuit 18. The polarity of the current resulting from this discharge is negative, and therefore the current I, flowing in the input terminal 3 is reduced so that the transistor 1 is rendered nonconductive and the tunnel diode 2 is shifted to the characteristic region below the maximum value I,,,. When the transistor 1 is rendered nonconductive, the potential at the collector electrode thereof increases, with the result that an output voltage appears at the output terminal 17. Such state corresponds to that in which the timing contact 26 is closed. When this timing contact 26 is closed, the transistor 88 is rendered nonconductive, so that the potential at the collector electrode thereof increases, with the result that the potential at the base electrode of the transistor 79 incorporated in the selector circuit 24 is increased so that the transistor 79 is rendered conductive. Thus, the amplifier transistor 116 provided in the switching circuit 25 has its base electrode grounded through the diode 122. At this point, the transistor 78 which constitutes the bistable flip-flop circuit together with the transistor 79 is in the nonconducting state, and the amplifier transistor 110 is rendered conductive with an output voltage appearing at the output terminal 17 of the operational circuit 18. Further, the transistor 112 is also rendered conductive to flow a current through the electromagnetic coils 113 and 114 so that the valve is opened to make the fuel injection possible. Simultaneously, the transistor 32 is rendered nonconductive with the result that the potential at the collector electrode thereof increases so that the capacitor 35 begins to be charged so that the terminal voltage thereof is increased to shift the transistor 36 from the nonconducting state to the conducting state. Thus, the potential at the emitter electrode of the transistor 36 is gradually increased in accordance with a lapse of time. This time-lapse signal voltage is imparted to the input terminal 9, resulting in a current which flows to the input terminal 3 through the resistor 13. In case the current I which is a combination of the signal current corresponding to the various conditions of the engine and the time-lapse signal current is lower than the maximum value I,,, of the tunnel diode 2, then all the input currents i are made to flow to the ground through the tunnel diode 2, and thus in this region the transistor 1 is maintained in the nonconducting state so that the fuel injection is continued. However, if the input current I, exceeds the maximum value I, of the tunnel diode 2, then the latter is brought into the negative region so that the internal impedance thereof increases to increase the terminal voltage. As a result, the potential at the base electrode of the transistor 1 is increased so that the conductive condition is established between the emitter and the collector electrodes thereof. At this point, the output voltage at the output terminal 17 becomes extinct. Thus, the transistors 110 and 112 are rendered nonconductive so that the currents flowing through the electromagnetic coils 113 and 114 are interrupted. Consequently, the valve is closed to interrupt the fuel injection. The time t in which the fuel injection is ended corresponds to that in which the input current I, reaches the maximum value I, of the tunnel diode 2. It depends upon the signal current which varies depending upon the various conditions of the engine. In this way, the quantity of injected fuel turns out to be a proper one which meets the various conditions of the engine.

When the crank shaft of the engine is rotated to a certain degree, the timing contact 26 is broken and subsequently the other timing contact 27 is made. Thus, the fuel-injecting operation is performed in a manner similar to that described above. In this case, the transistor 78 of the selector circuit 24 is rendered nonconductive while the transistor 79 is made conductive, so that the electromagnetic coils 119 and 120 are energized to open the valve.

In the foregoing embodiment, use was made of NPN- transistors, but it will be readily apparent to those skilled in the art that it is also possible to use PNP-transistors.

Description will now be made of the case where use is made of an operational amplifier, with reference to FIGS. 6a and 6b. This operational amplifier is of the ordinary type, and therefore detailed description thereof will be omitted. Applied to the signal input terminals are signal voltages which are obtained in accordance with the various conditions of the engine, and they are so set up as to decrease with increases in the rotational frequency N of the engine, the manifold negative pressure P and the temperature T. Further, the sawtooth wave voltage applied to the time-lapse signal input terminal 9 is one which rapidly drops to a negative voltage of a high magnitude upon the initiation of the input and thereafter gradually changes toward zero. Numeral 123 represents an operational amplifier, and 124 resistor.

In the aforementioned setup, normally the transistor 1 is rendered conductive with an input signal voltage which is obtained depending upon the various conditions so that no output voltage is available at the output terminal 17. However, if a negative voltage of a high magnitude is imparted to the time signal input terminal 39 at a point of time t when it is desired that the fuel injection be started, then the summed value becomes lower than the barrier voltage of the transistor 1 so that the latter is rendered nonconductive with the result that an output voltage appears at the output terminal 17. On the other hand, if the summed value becomes higher than the barrier voltage of the transistor 1 as a result of the gradual decrease of the time-lapse signal voltage, the transistor 1 is then rendered conductive so that the output voltage at the output terminal 17 becomes extinct. The time is changed like t i depending upon the magnitude of the input signal voltage corresponding to the various conditions, and thus the quantity of fuel to be supplied can be controlled as in the aforementioned embodiment.

We claim:

1. A fuel injection controlling system for internal combustion engines having a fuel control apparatus including an electromagnetic valve for controlling the amount of fuel delivered by the fuel supply for the engine comprising:

first means for generating a plurality of signal currents each being independent from one another having a magnitude corresponding to a respective condition from which the quantity of fuel to be supplied to said engine is determined;

second means for producing an output signal corresponding to an algebraic summation of the magnitudes of said independent signal currents; and

third means responsive to said output signal produced by said second means for controlling the opening duration of said electromagnetic valve, to thereby feed the proper quantity of fuel to said engine.

2. A fuel injection controlling system according to claim 1, wherein said first means includes a first circuit means for producing independent condition signal currents corresponding to the respective conditions of the engine operation, a second circuit means for independently producing a timing signal current which varies with a lapse of time from the starting point of fuel injection and a third circuit means for resetting the value of said timing signal current to a predetermined level at each starting point of the fuel injection and said second means includes an input terminal with a low input impedance for simultaneously receiving said independent signal currents, and an output terminal for producing said output signal corresponding to said algebraic summation, and wherein said third means includes a discriminator means for comparing the output signal produced by said second means with a predetermined discriminating level and for closing said electromagnetic valve at a desired time after the initiation of fuel injection, when said output signal produced by said second means reaches said predetermined level.

3. A fuel injection controlling system according to claim 2, wherein each of said first circuit means and said second circuit means includes a circuit having an output terminal for producing a voltage corresponding to the relevant condition and a resistor connected between said output terminal of said circuit and said input terminal of said second means, said resistor having a relatively high resistance higher than said input im' pedance of said second means.

4. A fuel injection controlling system according to claim 3, further including means for changing the resistance values of said resistors in response to a predetermined value of the negative pressure in the manifold of the engine.

5. A fuel injection controlling system according to claim 4, further including a correction means for correcting for a discontinuity in an input signal when said resistance values are changed.

6. A fuel injection controlling system according to claim 2, wherein said discriminator means comprises a transistor, the input terminals of which are constituted by the base-emitter electrodes thereof, and a tunnel diode connected between the base-emitter electrodes of said transistor in the same polarity therewith, whereby the transistor of said discriminator means which is normally in its conducting stat-e is rendered nonconductive at the beginning of the fuel injection and is rendered conductive when an input current reaches said predetermined level.

7. A fuel injection system according to claim 6, wherein the input terminals of said discriminator means are connected with the power source for said system through a capacitor so that a preparation current is supplied therethrough whereby said transistor in said discriminator means becomes conductive when said power source voltage is imparted thereto.

8. A fuel injection system according to claim 2, wherein said second means comprises an operation amplifier connected in series with said third means.

9. A fuel injection system according to claim 8, further including respective resistors for supplying said independent condition signals produced from said first means to said operational amplifier.

10. A fuel injection controlling system according to claim 1, wherein said first means comprises a negative pressure detector, an engine temperature detector, and a circuit for detecting the rotational frequency of said engine, each detector circuit producing an independent signal corresponding to a separate engine parameter.

11. A fuel injection controlling system according to claim 10, wherein said engine temperature detector comprises a thermistor-resistor series circuit the output of which is connected to a nonlinear clamping circuit whose output is, in turn, fed to said second means, whereby a signal representative of a nonlinear temperature sensitive: characteristic is provided by said first means.

112. A fuel injection controlling system according to claim 11, wherein said rotational frequency detector comprises a monostable multivibrator responsive to the interruption of pri- 

1. A fuel injection controlling system for internal combustion engines having a fuel control apparatus including an electromagnetic valve for controlling the amount of fuel delivered by the fuel supply for the engine comprising: first means for generating a plurality of signal currents each being independent from one another having a magnitude corresponding to a respective condition from which the quantity of fuel to be supplied to said engine is determined; second means for producing an output signal corresponding to an algebraic summation of the magnitudes of said independent signal currents; and third means responsive to said output signal produced by said second means for controlling the opening duration of said electromagnetic valve, to thereby feed the proper quantity of fuel to said engine.
 2. A fuel injection controlling system according to claim 1, wherein said first means includes a first circuit means for producing independent condition signal currents corresponding to the respective conditions of the engine operation, a second circuit means for independently producing a timing signal current which varies with a lapse of time from the starting point of fuel injection and a third circuit means for resetting the value of said timing signal current to a predetermined level at each starting point of the fuel injection and said second means includes an input terminal with a low input impedance for simultaneously receiving said independent signal currents, and an output terminal for producing said output signal corresponding to said algebraic summation, and wherein said third means includes a discriminator means for comparing the output signal produced by said second means with a predetermined discriminating level and for closing said electromagnetic valve at a desired time after the initiation of fuel injection, when said output signal produced by said second means reaches said predetermined level.
 3. A fuel injection controlling system according to claim 2, wherein each of said first circuit means and said second circuit means includes a circuit having an output terminal for producing a voltage corresponding to the relevant condition and a resistor connected between said output terminal of said circuit and said input terminal of said second means, said resistor having a relatively high resistance higher than said input impedance of said second means.
 4. A fuel injection controlling system according to claim 3, further including means for changing the resistance values of said resistors in response to a predetermined value of the negative pressure in the manifold of the engine.
 5. A fuel injection controlling system according to claim 4, further including a correction means for correcting for a discontinuity in an input signal when said resistance values are changed.
 6. A fuel injection controlling system according to claim 2, wherein said discriminator means comprises a transistor, the input terminals of which are constituted by the base-emitter electrodes thereof, and a tunnel diode connected between the base-emitter electrodes of said transistor in the same polarity therewith, whereby the transistor of said discriminator means which is normally in its conducting state is rendered nonconductive at the beginning of the fuel injection and is rendered conductive when an input current reaches said predetermined level.
 7. A fuel injection system according to claim 6, wherein the input terminals of said discriminator means are connected with the power source for said system through a capacitor so that a preparation current is supplied therethrough whereby said transistor in said discriminator means becomes conductive when said power source voltage is imparted thereto.
 8. A fuel injection system according to claim 2, wherein said second means comprises an operation amplifier connected in series with said third means.
 9. A fuel injection system accorDing to claim 8, further including respective resistors for supplying said independent condition signals produced from said first means to said operational amplifier.
 10. A fuel injection controlling system according to claim 1, wherein said first means comprises a negative pressure detector, an engine temperature detector, and a circuit for detecting the rotational frequency of said engine, each detector circuit producing an independent signal corresponding to a separate engine parameter.
 11. A fuel injection controlling system according to claim 10, wherein said engine temperature detector comprises a thermistor-resistor series circuit the output of which is connected to a nonlinear clamping circuit whose output is, in turn, fed to said second means, whereby a signal representative of a nonlinear temperature sensitive characteristic is provided by said first means.
 12. A fuel injection controlling system according to claim 11, wherein said rotational frequency detector comprises a monostable multivibrator responsive to the interruption of primary current flowing through a firing circuit, an integrating circuit connected in series with said monostable multivibrator and a clamping circuit connected in series with said integrating circuit, whereby a signal representative of the rotational speed of said engine will be delivered to said second means. 